The admissibility of expert evidence of mental disorder in criminal law and the application of the evidence act 1995 (NSW)

The Evidence Act 1995 (NSW) (hereafter EA) commenced on 1 September 1995. The Act sought to clarify and reform complex rules of evidence including the rules relating to the admissibility of expert evidence in criminal trials. In doing so however the legislation has raised its own complexities. The result is that the extent to which expert evidence may be admissible in the criminal trial requires a close analysis not only of the application of the opinion rule, but also other sections of the Act which impact upon it The application of expert evidence is particularly significant in the area of mental disorder in the criminal law, as demonstrated by reform of the law of diminished responsibility in New South Wales which (inter alia) emphasises a central role for the jury as the ultimate decision‐maker in the application of the defence. These developments in the law suggest a need for examination of the admissibility of expert evidence in trials where mental disorder of the accused, or sometimes the complainant or other witnesses, is raised. This article seeks to review the law of opinion evidence at common law and under the EA with a view to assessing the application of expert evidence in the field of mental disorder in the criminal law under the regime of the new legislation. The outcome reveals that each of the disciplines involved in this field need to come to grips with the application of the EA and the manner in which it shapes the relationship between evidence of mental disorder and the criminal law.